A study of the role of cellular and synaptic properties in the dynamic and flexible operation of oscillating neuronal circuits. We make use of two central pattern-generating circuits (CPGs) within the crustacean stomatogastric ganglion (STG),in a continuation of studies of this preparation begun in 1969. The stomatogastric system is the most extensively mapped neural circuit presently available. While not immediately related to health sciences, it allows us to ask basic questions about the design and function of oscillatory circuits, with implications for our understanding of motor and sensory circuits in vertebrate spinal cord and brain. 1. The role of synaptic time course in network dynamics: An assessment of the contribution of synaptic time-course to the temporal operation of the pyloric and gastric CPGs, two stomatogastric circuits that oscillate with about a 10 fold difference in frequency. 2. Modulation of cellular properties and network dynamics: An analysis of the modulation of active membrane properties in identified, single neurons and the consequent effects upon sub-circuit function. 3. Modulation of network dynamics and sensorimotor processing: A study of plasticity in sensorimotor pathways resulting from the modulation of cellular and synaptic properties in the stomatogastric motor circuits. These questions are addressed by interactive, electrophysiological, pharmacological and computer modeling techniques.